Corrosion resistant zirconium base alloys containing cb, cr, and sn



United States Patent CORROSION RESIS'iANT ZIRCONIUM BASE ALLOYS CONTAINENG Ch, Cr, AND Sn Octavian Eertea, Warren, James R. Gross, Kent, and

Stanley R. Seagle, Warren, Ohio, assignors, by mesne assignments, to National Distillers and Chemical Corporafion, a corporation of Virginia No Drawing. Filed May 23, 1961, Ser. No. 111,910

6 Claims. (Cl. 75-177) The invention relates to zirconium base alloys and Wrought zirconium base alloy products having an unusual combination of properties including high strength at both room and elevated temperatures, high resistance to corrosion and a low rate of H pickup as corrosion progresses.

There is an existing and unsatisfied need for wrought zirconium base alloy products having a combination of high strength, high corrosion resistance and low H pickup for fabrication into equipment used in nuclear reactor devices such as nuclear steam generator power plant equipment.

One commercial zirconium alloy containing 1.5% by weight tin, 0.10% by weight chromium, 0.05% by weight nickel, 0.12% by weight iron, and a maximum of 60 ppm. nitrogen, sometimes known as Zircaloy-Z, has been used somewhat extensively because of its low corrosion rate at elevated temperatures when in the presence of water or steam. The corrosion rate of this alloy, that is, its weight gain during corrosion, is about 37 mg./dm. in 750 -F.-1500 p.s.i.g. steam for 14 days, as compared with a corrosion rate for unalloyed zirconium under the same test conditions of about 31 mg./dm. However, the strength of Zircaloy-Z at elevated temperatures (18,000 p.s.i. yield strength at 900 F.) leaves much to be desired, as well as its rate of H pickup during corrosion.

The unsatisfied need for wrought zirconium base alloy products requires a minimum 35,000 p.s.i. yield strength at 0.2% oifset at 900 F. with 10% minimum room temperature tensile elongation in 2 inches, not possessed by Zircaloy-Z, combined with a corrosion rate comparable to that of Zircaloy-Z; or requires wrought zirconium base :alloy products having at least 50% greater strengths than the strengths of Zircaloy-Z at all temperatures accompanied by a comparable corrosion rate.

A number of zirconium base alloys are known, which include alloying elements as strengtheners that will satisfy the indicated high strength requirements. However, in each instance such known alloys have much higher corrosion rates than that possessed by Zircaloy-Z. Such known alloys therefore, do not satisfy the high corrosion resistance requirement. Further, such known alloys have a high H pickup as corrosion progresses, which also renders them unacceptable for many applications.

Accordingly, it is an object of the present invention to provide new zirconium base alloys and wrought zirconium base alloy products characterized by the unusual combination of properties, including, high strength with adequate ductility at room temperature, high elevated temperature strength, high corrosion resistance and low H pickup as corrosion progresses.

Furthermore, it is an object of the present invention to provide new zirconium base alloys and wrought products having 35,000 p.s.i. or more yield strength at 900 F. with good room temperature tensile elongation and high corrosion resistance.

Furthermore, it is an object of the present invention to provide new zirconium base alloys and wrought products having strengths at all temperatures at least 50% greater than the strengths at the same temperatures of Zircaloy-Z and having a corrosion rate comparable to the 37 rng/dm. rate in 750 F.-'1500 p.s.i.g. steam for 14 days, of Zircaloy2'.

3,205,070. Patented Sept. 7, 1965 Also, it is an object of the present invention to provide new zirconium base alloys and wrought products having the same or greater strengths as Zirca-loy-Z, but having a lower hydrogen pickup than Zircaloy-Z when compared on either a per day or a per weight gain basis.

Finally, it is an object of the present invention to provide new zirconium base alloys and wrought products which avoid the difiiculties heretofore encountered with prior art zirconium base alloys, and which new alloys satisfy the existing need in the art for an heretofore unobtained unusual combination of strength and corrosion resistance properties.

We have discovered a novel series of zirconium base alloys and wrought products having compositions in particular ranges which satisfy the need. High strength is achieved primarily by the addition of columbium as a. strengthening agent, and tin or chromium or both also may be added for this purpose. In a Zr-Cb-Sn-Cr alloy, the minimum effective amount of columbium to achieve strengthening is 1% and may range from 1 to 3% by weight. When the columbium is 1% in such alloy the Sn and Cr contents must be higher to achieve the minimum 35,000 p.s.i. yield strength at 0.2% offset at 900 F. With 3% columbium, the amounts of one or more of Sn and Cr may be reduced and the minimum 35,000 p.s.i. yield strength at 900 F. approached or achieved.

Although Zr-Cb-Sn-Cr alloys with a minimum of 1% Cb may not have a desired minimum 35,000 p.s.i. yield strength at 900 F., nevertheless such alloys have a low or non-detected H pickup in 14 day corrosion tests,

which is an extremely advantageous property. The tin content, in accordance with the invention, may range from the 0.3% to 3% by weight while the chromium content may range from 1% to 3% by Weight.

The desired ductility may be developed in these high strength alloys by the particular heat treatment to which the particular alloy is subjected. Normally, the greatest strength may be developed by heating followed by air cooling. However,. greater room temperature ductility usually may be developed it the material is furnace cooled, rather than air cooled, at the sacrifice of some strength.

Material which has been furnace cooled however normally is subject to a higher corrosion rate. That is, the worst conditions with respect to corrosion resistance result in material which has been furnace cooled.

An objectionable high corrosion rate for such alloys and wrought products resulting from either furnace cooling :or air cooling the material, maybe corrected by omitting the usual final pickling operation in the production of hot rolled 'bar and sheet products and substituting a-final cold working operation for the omitted pickling operation, or by using a final cold working operation following a pickling operation as described in our copending application S.N. 75,9311 filed December 15, 1960, now abandoned.

The ability to reduce the high corrosion rate of the al'-' loys from an unacceptable high value to an acceptable low value apparently depends upon the presence of columbium in the alloys; and the extent to which' the cor rosion rate may be reduced appears to depend upon the amount of columbium present.

Also, the zirconium base alloys of the invention are further characterized by reduced H pickup as corrosion progresses.

The foregoing objects and the advantages apparent to those skilled in the art from the following description may be obtained, the stated results achieved, and the described .ditliculties overcome, by the discoveries, principles,v compositions, particular composition ranges, alloys and wrought products which comprise the present invention} the nature of which are set forth below-i'llustrative of the best modes in which applicants have contemplated applying the principlesand which are particularly and distinctly pointed out and set forth in the appended claims forming part hereof.

The alloys of the present invention are preferably prepared from 140 BHN reactor grade zirconium sponge and that the alloys are close to such nominal or intended compositions. In Table 1, properties are indicated for different heat treatments including air cooling (AC) or furnace cooling (FC) which may be used, selectively, in order to commercially pu-re alloying elements. In practice, the 5 achieve some desired value of strength or ductility.

Table I Room temperature properties 900 F. properties Heat No. Composition Heat treatment UTS, k.s.i. YS, 0.2% Elong. 1n UTS, k.s.l. YS, 0.2% Elong., oil, k.s.i. 1", percent 05, k.s.i. percent 28075 Zircaloy-Z 78 52 27 33.8

121 88 1-. X4270 Zr-1Sn-3Cr-3Cbg 5g 41 32. a

'1 9-: t pit-1383---- m-lSn-lCr-Cb 1 g 2 31 21 40. o

a U8 7 .1. DM1384 zr-ssn-sor-icb H5 82 u E 40 a3 25. 0 x-22s0 Zr-8Sn-1Cr-3Cb 3% 5 57 42 27. 0 DM-127L Zr- ).3Sn-1Cr-3Gb- 94 71 21. 8 55 3. 28. 5 X-2228 Zr-2Sn-2Cr-2Cb 98 75 18. 5 37 22 58. S

1 FC to 900 F..AC. alloys are preferably double melted by the usual consumable electrode arc melting procedures in a water cooled copper crucible and in a vacuum or an argon atmosphere. The alloying elements are added by compacting with the zirconium sponge.

The alloys of the present invention after melting may be processed in the usual manner and forged and hot rolled to form the desired semi-finished or finished wrought products such as bar, plate, sheet, strip or tube products. The hot rolled or hot worked material is then annealed in the usual manner. A final cold working operation following annealing is performed to impart a low corrosion rate characteristic to the product as by finally machining bar products.

In the case of cold rolled sheet or strip material, hot rolling may be performed in the usual manner followed by annealing and pickling of the hot rolled material. Then the pickled hot rolled material is cold rolled to desired gauge with a cold rolling constituting the final cold working operation in order to impart the low corrosion rate characteristic to the material.

Room and elevated temperature tensile properties of The air cooled specimens in Table I with the exception of Heat DM1384, have greater room temperature strength than the furnace cooled specimens. Similarly, the furnace cooled specimens in Table I with the exception of Heat No. DM1384, have greater ductility than the air cooled specimens.

The high temperature strengths of the alloys of Table I, with the exception of Heat Nos. DM13=83 and X2228, approach or exceed the desired 35,000 p.s.i. yield strength at 0.2% offset at 900 F. with 10% minimum room temperature tensile elongation, or have at at least greater strengths than the strengths of Zircaloy-2 at all temperatures accompanied by a comparable corrosion rate as will be indicated below. Heat Nos. DM=1383 and X2228, however, approach 50% greater strength at room temperature, and have 16.5% greater 900 F. strength than Zir-. caloy-Z.

The corrosion rates of the alloys of the present invention including high unacceptable corrosion rates for materials in pickled condition, and low corrosion rates for the materials processed to include a final cold working operation, are given in Table II below.

Table 1I.The weight gain of Zr-Sn-Cb-Cr Alloys in 750 F.-1500 p.s.i.g. Steam Heat No. Composition Heat treatment Surface Weight gained mg'ldm'Lqfioo F" 1500 India Steam preparation 14 days 28 days 42 days 56 days days 28128 Zircaloy-2 1550F.,%hr.-AC sg igggg X4279 zplsnacpgcb l525F.,1l1r.FC. fg fg 199.0 265.5 326.0 1525 iifSiiliSaiiIj it? 153-8 219-7 284-2 W438, dittiifisrx: 2&2

l C {gfgffigg 50.2 82.0 110.0 W438, Zmsmomcb irfZiriiiijjjj 7%;3 293's 'r -{5 g::: 35, 3 181.0 214.9 362.4 H280 1W --itlfra::: 2%? 22:3 53:? are 176.5

1425F.,1m.-Ao {g 22:3 69.6 113.0 Dir-1271 Zr-0.3Sn-1Cr3Cb 1425:F"1hr' m n 2%? 12%;; 55:5 Tim-'5 1425 F.,1hr.-AC nhgi g fig- 1475F.,1hr.-FO X-2315 Zr-2Sn-2Cr-2Cb 14750 FAMFAC g j gii gzg 1 Powdery film. 2 Black adherent film.

Zr-Sn-Cr-Cb alloys of the invention are given below in Table I. For comparative purposes, similar properties of Zircaloy-2 are also given in Table 1. Each of the alloys is referred to by its nominal or intended c0rnp0sition, chemical analyses of the various alloys indicating It is significant from the data in Table II that the finally cold Worked specimens (machined) having the greatest amount of columbium in their compositions have the lowest corrosion rates, approaching the 37 mgJ/drn? corrossion rate of Zircaloy-Z; have the greatest strength (Table I); and have the greatest decrease in corrosion rate when the pickled and finally cold worked specimens are compared (see values for Heat Nos. X2279, X2280 and 6 The discovery that the unusual combination of properties could be obtained in 3-20% Cb binary zirconium alloys was entirely unexpected since heretofore it was believed that binary Zr-Cb alloys containing 3% or DM1271)' 5 more of Cb were not commerci ally acceptable because Talia {5 3 nlldlcaze tlhat g of the high corrosion rate heretofore thought to charm mvo V1 f 0mg a mos a Ways lmpar S e acterize Zr-Cb alloys containing 3% or more of Cb. greater corrosion resistance. h

The effect of steam corrosion on the hydrogen pickup Alt Dug]? the corroslon rates of the .vanous alloys of the alloys of the invention is indicated in Table Ill be- 10 tabulated m Tble IV are apparently. i and low The Table 111 data shows that hydrogen Pickup ceptable even in the cold rolled condition, these rates either is not sufi'icient to be detected, or is at a lower rate actually are Probably the hlghest value that can Posslbly a for Zi 1 2 That is, the hydrogen pickup f occur as a result of heat treatment. The eifect of heat the alloys of the invention is less than that of Zircaloy2 treatment on the corrosion resistance f t Z -5C When compared on either a per day or a per weight gain Zr-15cb alloys in the Pickled condition is Shown n basis. Table V below.

Table IIl.-The efiecz of steam corrosion 0n the hydroge pickup of Zr-Sn-Cb-Cr alloys Hydrogen pickup, ppm. after steam corrosion, 750 F., 1500 Surface p.s.i.g. Heat No. Composition Heat treatment preparation 14 days 28 days 42 days 56 days. 70 days Q Pickle ND 2 1550 F., l hr.-FC

DM-1384 Zr-3Sn-1Cb-3Cr k 1475 F., 1 hr.-FO X-2279 Zr-1Sn-3Cr-3Cb 1 {147? F., 1 hr.-AC-

{1425" F., 1l1r.-FO P DM-1383 Zr-1Sn-1Cr-1Cb 1425" F., 1 h!.-AC

1425 F., 1 hL-FC DM-1271 znoiasn-rcr-scbt {1425F 1 hr.-AC

X-22s0 Zr-3Sn-10r-3Cb 1425F., 1hr.-FC X-2315 Zr-2Sn-2Cr-2Cb 1475 F., 1 hI'.FC

2s1o1- Zircaloy-2; 1550F.,%hr.AC

fig?

1 Weight gain for Zircaloy-2, mgJdm. 2 N.D.-Not detected.

Table V.Efiect of heat treatment on the corrosion resistance of Zr-SCb and Zr-1'5Cb (pickled) Weight Gain, 14 days Treatment 1100 F., 96 hr.-FC 1000 F., 1 hr.-BQ 1 1600 F., 1 hr.-BQ, 9 1500 F., l hr.-FC to 800 1450 F., 2 hr.-FC to 800- -v 1300 F., 2 tin-F0 to 800. 1150 F., 3 hr.-FC to 800.

1 Brine quench.

Table I V.Zr-Cb alloys Weight gain, mgJdmfi, 14 Room temp. properties 900 F. properties days in 750 F. 1500 p.s.i.g., steam Heat N0. Comb. Heat treatment YS, 0.2% Elong. UTS, E1ong.,

UTS ofi, k.s 1 in 1", k.s.i. YS, k.s.i. percent Pickled As-machined' percent 1475" F. 1 hr.-AO 109 86 4.0 Zr-3Cb 14750 hr 78 56 m 3 71 53 10. 0 70. 7 53. 9 Zr-5Cbi 1100 F., 96 hr FC 63 1 18 36 28 27. 2 103. 6 2 50 105 96 l 11 50 42 13. 5 110. 1 2 70 107 99 1 6. 5 53 48 18. 3 118. 7 2 70. 6 102 1 9. 5 G0 53 20. 0 127 2 87 1 In 2', percent. 2 Cold rolled.

7 The data in Table V demonstrate that by changing heat treatment, the corrosion rate of the material in the pickled condition can be substantially reduced; and inaccordance with the data in Table IV, the corrosion rate values can be reduced further in finally cold worked material to values comparable to the corrosion rate of Zircaloy-Z.

Accordingly, the new zirconium base alloys and wrought zirconium base alloy products of the presentinvention provide compositions and products that have an unusual combination of properties including high strength, high corrosion resistance and low H pickup; and as such provide products which eliminate ditficulties and satisfy existing requirements and needs in the art. In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes herein and not for the purpose of limitation, and are intended to be broadly construed.

Having now described the invention, the features, discoveries and principles thereof, the combined characteristics of the new zirconium base alloys and products, and the new and useful results obtained thereby; the new and useful compositions, alloys, products, and discoveries, and reasonable mechanical equivalents thereof, obvious to those skilled in the art, are set forth in the appended claims.

We claim:

' 1. An alloy composed of 1-3% by weight Cb, 1-3% by weight Cr, 0.3-3% by weight Sn and the balance zirconium with incidental impurities, characterized by having corrosion resistance such that it gains 78.9 mg./dm. or less, when exposed for 14 days to 750 -F.-1500 p.s.i.g.

2. An alloy composed of 3% by weight Cb, 1-3% by weight Cr, 0.3-3% by weight Sn and the balance zirconium with incidental impurities, characterized by having 71,000-87,000 p.s.i. yield strength at 0.2% offset and 18.021.8% elongation in 1" at room temperature, 29,000-42,000 p.s.i. yield strength at 0.2% offset and at 900 F., and 48.8 mg./dm. or less weight gain when exposed for 14 days to 750 F.-l500 p.s.i.g. steam.

3. An alloy composed of 3% by weight Cb, 1% by weight Cr, 0.3% by weight Sn and the balance zirconium with incidental impurities, characterized by having 71,000 p.s.i. yield strength at 0.2% offset and 21.8% elongation 8 in 1" at room temperature, 33,000 p.s.i. yield strength at 0.2% offest and at 900 F., and 44.9-48.8 mg./drn. weight gain when exposed for 14 days to 750 F.-l500 p.s.i.g. steam. I

4. An alloy composed of 3% by weight Cb, 1% by weight Cr, 3% by weight Sn and the balance zirconium with incidental impurities, characterized by having 87,000 p.s.i. yield strength at 0.2% offset and 18.5% elongation in 1" at room temperature, 42,000 p.s.i. yield strength at 0.2 oflset and at 900 F., and 41.8-45 mgldm. weight gain when exposed for 14 days to 750 F.-1500 p.s.i.g. steam. 5. An alloy composed of 3% by weight Cb, 3% by weight Cr, and 1% by weight Sn and the balance zirconium with incidental impurities, characterized by having 74,000 p.s.i. yield strength at 0.2% oifset and 18% elongation in l" at room temperature, 29,000 p.s.i. yield strength at 0.2% ofiset and at 900 F., and 47.0-47.6 mgJdm. weight gain when exposed for 14 days to 750 F.-1500 p.s.i.g. steam.

6. An alloy composed of 1-3% by weight Cb, 13% by weight Cr, 0.3-3% by weight Sn and the balance zirconium with incidental impurities, characterized by having no detectable hydrogen pickup when exposed for 14 days to 750 F.-1500 p.s.i.g. steam.

References Cited by the Examiner UNITED STATES PATENTS 2,307,960 1/43 Schafer 75-177 XR 2,772,964 12/56 Thomas et al. 75177 FOREIGN PATENTS 831,202 3/ Great Britain.

OTHER REFERENCES Miller, Zirconium, 2nd Edition, pages 231 and 232, published by Academic Press Inc., 111 Fifth Avenue, New York 2, NY.

Miller, Zirconium, 2nd Edition, published by Butterworths Scientific Publications, 1957, pages 374-375 relied BENJAMIN HENKIN, Primary Examiner.

MARCUS U. LYONS, RAY K. WINDHAM, DAVID L. RECK, Examiners. 

1. AN ALLOY COMPOSED OF 1-3% BY WEIGHT CB, 1-3% BY WEIGHT CR, 0.3-3% BY WEIGHT SN AND THE BALANCE ZIRCONIUM WITH INCIDENTAL IMPURITIES, CHARACTERIZED BY HAVING CORROSION RESISTANCE SUCH THAT IT GAINS 78.9 MG./DM.2 OR LESS, WHEN EXPOSED FOR 14 DAYS TO 750*F.-1500 P.S.I.G. 